WO2011002511A1 - Multi-phasic implant device for the repair or replacement of cartilage tissue - Google Patents
Multi-phasic implant device for the repair or replacement of cartilage tissue Download PDFInfo
- Publication number
- WO2011002511A1 WO2011002511A1 PCT/US2010/001878 US2010001878W WO2011002511A1 WO 2011002511 A1 WO2011002511 A1 WO 2011002511A1 US 2010001878 W US2010001878 W US 2010001878W WO 2011002511 A1 WO2011002511 A1 WO 2011002511A1
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- WIPO (PCT)
- Prior art keywords
- tissue
- cartilage
- gradient
- matrix
- bone
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Definitions
- the present invention pertains to medical or surgical devices intended to be implanted into the body of a living being.
- the devices are intended to repair or replace lost or damaged tissue, and in particular, cartilage or cartilage-like tissues.
- Cartilage is found throughout the body, such as in the supporting structure of the nose, ears, ribs (elastic cartilage), within the meniscus (fibrous cartilage), and on the surfaces of joints (hyaline cartilage or articular cartilage).
- a joint is a bending point where two bones meet. The knee, hip, and shoulder are the three largest joints.
- hyaline The specialized covering on the ends of bones that meet to form an articulating joint. It is the cartilage that is damaged and wears as one ages, or sustains an injury. Articular cartilage is unique amongst the body tissues in that it has no nerves or blood supply. This means that damage will not be felt until the covering wears down to bare underlying bone. Bone is very sensitive and the sharp pain of arthritis often comes from irritation of bone nerve endings and since human tissue has a very limited capacity to heal without a blood supply, articular cartilage cannot repair itself effectively.
- Articular cartilage tissue covers the ends of all bones that form diarthrodial joints.
- the resilient tissues provide the important characteristic of friction, lubrication, and wear in a joint. Furthermore, it acts as a shock absorber, distributing the load to the bones below. Without articular cartilage, stress and friction would occur to the extent that the joint would not permit motion.
- articular cartilage has only a very limited capacity to regenerate. If this tissue is damaged or lost by traumatic events, or by chronic and progressive degeneration, it usually leads to painful arthrosis and decreased range of joint motion.
- Articular cartilage repair following injury or degeneration represents a major clinical problem, with treatment modalities being limited and joint replacement being regarded as appropriate only for the older patient.
- Anti-inflammatory medication Aspirin was the first anti-inflammatory medication in the world. This was followed in 1950 by cortisone (steroidal medication) used orally or by injection. (Extensive use of cortisone not only has a wide variety of harmful effects, but is also believed to harm cartilage.) Later the non-steroidal drugs such as Motrin came along. These were safer than Aspirin and cortisone but had potent side effects, especially causing bleeding within the stomach and intestinal ulcers. These complications led to the development of the COX-2 inhibitor drugs, Celebrex and Vioxx. While much safer and seemingly more effective, Vioxx was found to have significant cardiac side effects and is no longer available. With certain precautions, Celebrex is still widely used. However, these anti-inflammatory medications only treat the symptoms of cartilage damage and arthritis and do not promote repair.
- Viscosupplementation is a procedure that involves the injection of gel-like substances (hyaluronates) into a joint to supplement the viscous properties of synovial fluid.
- hyaluronate injections are approved for the treatments of osteoarthritis of the knee in those who have failed to respond to more conservative therapy, Once again, this procedure only treats the symptoms of cartilage damage and arthritis and does not promote repair.
- Chondroplasty is a term referring to the arthroscopic smoothing of unstable articular surfaces either with mechanical shaving or thermal devices. While not a restorative measure, so called debridement can be useful in reducing irritating cartilage debris that breaks off in the joint or causes catching or grinding sensations. The resulting improvement in the control of inflammation can last for several years. But this is not a final solution as the degenerative process continues to wear away at the articular cartilage.
- Autogenous articular cell implantation can be used for large, shallow defects, which do not involve the subchondral bone.
- cartilage cells collected from the patient and grown to many millions through cell culture techniques are injected into the joint, under a membrane that has been attached to the cartilage surface.
- the window of opportunity for this procedure is often missed, as the few clinical symptoms showing the need for this treatment are not evident until the defect deepens to involve the underlying bone, thus the damage encountered upon detection is frequently too extensive for repair through ACI.
- Microfracture The goal of this arthroscopic technique is to improve the blood supply to the bare areas of the joint by creating tiny perforations in the underlying bone.
- the resulting bone marrow bleeding carries powerful growth stimulating factors found in platelets as well as stem cells to the damaged area creating what is referred to as a super-clot.
- Healing and repair follow over several weeks.
- the fibrocartilage tissue can temporarily return function for activities such as running and a sport play, but ultimately fails, as fibrocartilage is unable to mechanically share and dissipate loading forces as effectively as the original hyaline cartilage.
- Fibrocartilage is much denser and isn't able to withstand the demands of everyday activities as well as hyaline cartilage and is therefore at higher risk of breaking down.
- Osteochondral transplantation i.e.
- mosaioplasty involves transportation of tissue plugs from one location of the knee to another. Special instrumentation has been devised to harvest plugs of articular cartilage and its supporting bone from the patient's own joint. The harvested tissue is then transported to the damaged site where it is inserted into prepared holes. Several plugs can fill up rather larger defects and will grow to re-supply a new joint surface. Unfortunately, this procedure leaves defects of equal or worse proportions elsewhere and often the harvested tissue is not viable due to the traumatic harvesting procedure.
- Applicants have made the surprising discovery that in effecting the repair of cartilage defects, prior art synthetic implants and synthetic bi-phasic implant devices failed to recognized the need to ignore the normal histological and mechanical gradient of the articular cartilage, and instead focused on the limited cell population surrounding the defect and its slow rate of tissue formation within the devices resulting from this sparse population of cells.
- the prior art synthetic implants mistakenly focused on speeding up the rate of cell migration within the scaffold in hopes of getting tissue to form rapidly throughout the device prior to collapse of the scaffold. This increased rate of cell migration was done using chemotactic ground substances such as hyaluronic acid, cell seeding or biologies.
- the uninvolved host tissue that is, the normal tissue adjacent to and surrounding the defect site that is not involved with the defect, is able to influence the activities of cells that migrate into and establish themselves at the periphery of a scaffold placed into the defect.
- the cells of the uninvolved tissue, along with the extracellular matrix of the uninvolved host tissue adjacent to the periphery of the implanted scaffold are already established as hyaline cartilage and thus mechanically and chemically react to stresses appropriately.
- mechanical signal transduction the established host tissue is able to influence the phenotype and extracellular matrix produced by the adjacent cells in the scaffold thus producing the desired hyaline cartilage.
- cartilaginous tissues perform specialized functions under normal physiological conditions. Anomalous mechanical loading of these tissues often leads to pathology. For example, the lack of mechanical stimulation of a joint leads to suppression of proteoglycan synthesis and release of mediators responsible for degradation of cartilage matrix components. This is believed to be the cause of collapse or dimpling of the newly formed cartilage seen with prior art devices.
- fibrocartilage that collapses as the matrix degrades and the tissue experiences stress loading.
- synovial fluid is a thick, stringy fluid found in the cavities of synovial joints. Synovial fluid reduces friction between the articular cartilage surfaces as well as providing cushioning during movement. The inner membrane of synovial joints is called the synovial membrane and it secretes synovial fluid into the joint cavity.
- This fluid forms a thin layer (about 50 microns thick) at the surface of cartilage and seeps into the micro-cavities and irregularities in the articular cartilage surface, filling all empty space thus presenting a uniform, smooth surface.
- the fluid in the articular cartilage effectively serves as a synovial fluid reserve, during movement; the synovial fluid held in the cartilage is squeezed out mechanically to maintain a layer of fluid on the cartilage surface. This so called weeping lubrication ensures that increased friction does not occur as some of the lubrication fluid is swept away during joint movement.
- Synovial tissue is composed of vascularized connective tissue that lacks a basement membrane. Two cell types (type A and type B) are present: Type B cells produce synovial fluid. Synovial fluid is made of hyaluronic acid and lubricin, proteinases, and collagenases. Synovial fluid exhibits non-Newtonian flow characteristics. The viscosity coefficient is not a constant, the fluid is not linearly viscous, and its viscosity increases as the shear rate decreases.
- synovial fluid Almost all of the protein constituents of synovial fluid are derived from plasma.
- the passage of plasma proteins to synovial fluid is related to the size and shape of the protein molecule. Most proteins with molecular weights less than 100,000 daltons are readily transferred from one fluid space to another.
- synovial fluid is a plasma dialysate modified by constituents secreted by the joint tissues.
- the major difference between synovial fluid and other body fluids derived from plasma is the high content of hyaluronic acid (mucin) in synovial fluid.
- hyaluronan a polymer of nonsulfated polysaccharides composed of D-glucuronic acid and D-N-acetylglucosamine joined by alternating beta-1 ,4 and beta-1 ,3 glycosidic bonds.
- Hyaluronan is synthesized by the synovial membrane and secreted into the joint cavity to increase the viscosity and elasticity of articular cartilage and lubricates the surfaces between synovium and cartilage. Both fibroblasts beneath the synovial membrane intima and synovial membrane-lining cells produce this mucopolysaccharide constituent of synovial fluid.
- Synovial fluid is believed to have two main functions: to aid in the nutrition of articular cartilage by acting as a transport medium for nutritional substances, such as glucose, and to aid in the mechanical function of joints by lubricating the articulating surfaces.
- Articular cartilage has no blood, nerve, or lymphatic supply.
- Glucose for articular cartilage chondrocyte energy is transported from the periarticular vasculature to the cartilage by the synovial fluid.
- Synovial fluid contains lubricin secreted by synovial cells.
- Synovial fluid is chiefly responsible for so-called boundary-layer lubrication, which reduces friction between opposing surfaces of cartilage.
- synovial fluid helps regulate synovial cell growth.
- Synovial fluid serves many functions including: reducing friction by lubricating the joint; absorbing shocks; and supplying oxygen and nutrients to, as well as removing carbon dioxide and metabolic wastes from, the chondrocytes within articular cartilage.
- Normal synovial fluid does not clot but may exhibit thixotropy, the property of certain gels to become fluid when exposed to shear forces such as shaking. On standing at room temperature, normal synovial fluid may assume gelatin-like appearance, characterized by higher viscosities. When shaken it will assume a normal fluid nature. Many enzymes have been found in the normal synovial fluid. Alkaline phosphatase, acid phosphatase, lactic dehydrogenase, and other enzymes are present in detectable quantities. Enzymes enter the synovial fluid directly from the plasma or may be produced locally by the synovial membrane or released by synovial fluid macrophages. Synovial fluid also contains phagocytic cells that remove microbes and the debris that results from normal wear and tear in the joint.
- Some prior art devices utilize fluid impermeable layers at the cartilage surface, the bone/cartilage interface, or both locations, or have rigid articular cartilage regions resistant to receiving fluid from the synovial space. These types of structures serve as barriers that prevent the normal transfer of essential elements from the synovial fluid, into and out of the cartilage region. What is needed is a device capable of facilitating joint fluid therapy to the chondrocytes within the defect.
- Joint fluid therapy encompasses delivering, receiving, accumulating and controlling the location of desirable factors or molecules present in the synovial fluid while also delaying or preventing destructive factors, such as digestive enzymes, from prematurely degrading the matrix. These desirable factors or molecules can be those naturally occurring within the synovial fluid or biologically active agents administered into the synovial fluid.
- one embodiment is directed to a multi-phasic prosthetic device for repairing or replacing cartilage or cartilage-like tissues.
- Such prosthetic devices are useful as articular cartilage substitution material and as a scaffold for regeneration of articular cartilaginous tissues.
- This invention includes implantable biphasic devices for the repair of tissues of a living being, especially, cartilaginous tissue defects.
- the device has a first region and a second region, each being specific for the growth of a particular tissue type.
- the first region is specific for cartilage tissue growth
- the second region is specific for bone growth.
- the device is an electro-kinetic implant, in which at least a portion of the device features two juxtaposed materials that form a malleable matrix, where the first material presents a positively charged surface, and the second material presents a negatively charged surface.
- the malleable matrix is deformed under the application of pressures, such as may occur while implanted in a living being, an electrical potential is produced as a result of interactions, and interruptions, between the charged surfaces of the first and second materials.
- the malleable material will be malleable while hydrated, though it may be rigid, or at least capable of being handled without deformation, while in a dry state.
- the malleable material may exhibit an elastic property, tending to return to its original shape after having been deformed.
- the first material of the malleable materials may be a particulate, especially a fibrous particulate
- the second material of the malleable material may be a hydrogel, such that the particulate is suspended within the hydrogel, and upon deformation, the hydrogel and particulate move relative to each other.
- the malleable material may be porous.
- the materials may be ceramics, natural polymers, synthetic polymers, or combinations thereof.
- the charges in the charged surfaces may be the result of exposure of the constituent materials to acidic or basic environments, plasma gas, or a result of the attachment of charged substances to the materials.
- the first and second materials of the malleable material are collagen, with the first collagen material, such as a fibrous collagen, presenting a positively charged surface, and the second collagen material, such as a hydrogel presenting a negatively charged surface.
- the charged surfaces of the fibrous collagen and hydrogel collagen may be created by exposing each of the collagens to solutions, where one collagen is exposed to a solution having a pH above the isoelectric point of the collagens, and the other collagen is exposed to a solution having a pH below the isolectric point of the other collagen.
- Another aspect of the invention provides for the transmission of forces and loads throughout a malleable matrix component making up at least a portion of the implantable device.
- the malleable matrix component is created having a first and second material, where the first material is a hydrogel and the second material is an
- the hydrogel component may be collagen, or hyaluronic acid, and the fibrous component may be collagen or chitosan.
- the malleable matrix component is able to provide joint fluid therapy to the cells or tissue within the implant device as it is arranged to transmit forces throughout the entire, or at least substantially the entire volume, of the malleable matrix component, as forces applied will cause a vortex ring or gyre due to the interactions of the interconnected fibers pulling on each other, as they are displaced within the hydrogel material.
- the three-dimensional transmission of forces throughout the malleable material will result in the malleable material, or at least the hydrogel component of the malleable material, receiving and accumulating desirable factors or molecules from surrounding fluids, which may be utilized by cells within the device.
- the malleable material is one phase of a biphasic device, and corresponds to the cartilage region, thus the malleable material may be attached to a rigid base corresponding to the bone region.
- the implant provides for the systematic tissue conduction and growth from the surrounding cartilage tissue, and retards the formation of tissue in the interior of the implant. In this manner, it is believed that the growth of the incorrect type of tissue can be avoided, and better ensure that only the desirable hyaline cartilage is formed.
- the device may include a gradient, where the gradient is arranged to retard the tissue formation most at or near the center of the implant (when viewed top down), and transitions to little or no retardation of tissue formation towards the perimeter of the implant, adjacent to normal cartilage tissue.
- the gradient may be in the form of a circular gradient, and may be uniform throughout the device from upper surface to lower surface, or alternatively may vary from top to bottom.
- the gradient may be a smooth transition or gradual gradient, or alternatively a stepwise gradient having well defined regions within the gradient.
- the gradient may be a concentration gradient, such as biologically active agents, additives, or combinations thereof.
- the gradient may be a physical gradient, such as porosity, density, expansion, swelling, elasticity, hardness, compressibility, and combinations thereof.
- the gradient may be a material gradient, or chemical gradient, such as molecular weight, cross-linking,
- the gradient may be part of the first phase of a multiphasic device, and corresponds to the cartilage region, and may be attached to a rigid base corresponding to the bone region.
- the multiphasic implant provides for the transmission or conduction of pressure forces through the device, down to the underlying bone tissue below the device; in this manner, bone tissue loss below the device, such as may occur due to stress- shielding, may be minimized or avoided.
- an implant device capable of transmitting such forces would present a bone region presenting a porous material and a rigid penetrating force conductive material capable of transmitting the forces received from a malleable cartilage region to the underlying tissue.
- the forces to be transmitted may be hydrostatic and directed through channels running through the bone region material, or alternatively force transmission may be in the form of kinetic pressure pulses through the rigid conductive material arranged in the bone phase.
- the rigid conductive material may be in the form of columns arranged perpendicular to the top and bottom surfaces of the implant, and may flare out to a wider dimension at the junction with underlying bone.
- the rigid conductive material may be in the form of a rigid multi-facetted web structure oriented perpendicular to the top and bottom surfaces of the implant.
- the rigid conductive material is a wedge or cone that transmits the forces through the implant to the underlying bone, but may also transmit some forces laterally as an outward force to the porous bone region material.
- the multiphasic device capable of transmitting pressure forces presents at least a first material in the form of at least two porous rigid scaffolds, where the first material is separated by at least a second material in the form of a malleable elastic hydrogel, and where the hydrogel is capable of transferring hydrostatic pressure pulses through the bone region of the device in order to prevent bone voids from forming in external underlying bone tissue.
- the various embodiments described herein may be at least partially or completely resorbed by the living being.
- the various embodiments described herein may also feature drugs, biologically active agents, or other additives in all or at least a portion of the device.
- Fig. 1 is a perspective depiction of a circular gradient.
- Fig. 2 is a cross-section depiction of the circular gradient of Fig. 1.
- Fig. 3 is a perspective depiction of a circular gradient having a tapered construction from upper surface to lower surface.
- Fig. 4 is a perspective depiction of a circular gradient having an hour-glass shape, wherein the gradient zones are wider in the upper and lower surfaces, and featuring a narrow mid-section.
- FIG. 5 and 6 are perspective depictions of multiple circular gradients within the same device
- Fig. 7 is a cross-sectional depiction of a biphasic device as found in the prior art, having a cartilage region including a gel or porous material.
- Fig. 8 is a cross-sectional depiction of a biphasic device, having a cartilage region arranged as a web or matrix, where the web or matrix is able to telegraph applied forces through substantially all of the cartilage region, by the movement of the web or matrix constituents in a manner analogous to a vortex ring, or gyres.
- Fig. 9 is a 1-year histology slide of a repair site having had a prior art biphasic implant device implanted, after the device has been completely absorbed, wherein stress shielding is evident.
- Fig. 10 is a cross-sectional depiction of an implant embodiment that is arranged to transmit forces or loads through the device to underlying tissue below, using a rigid central column.
- Fig. 1 1a and b are cross-sectional depictions of another implant embodiment arranged to transmit forces or loads through the device using a stiff, multifaceted web structure and filler porous material.
- Fig. 12 is a cross-sectional depiction of an implant embodiment that is arranged to transmit forces or loads through the device using a rigid central conically shaped center post.
- Fig. 13 is a depiction of a multi-layered cylinder including various material thicknesses and densities, where the layers can serve to transmit forces or loads through the device to underlying tissue below.
- FIG. 14a and b are depictions of a multi-layered cylinder material having swellable properties upon hydration, and capable of transmitting forces hydraulically through the device to the underlying tissue below.
- the device is to provide the means by which hyaline cartilage tissue can be conducted across a tissue specific first scaffold region by controlled migration of chondrocytes and/or cartilage precursor cells.
- the scaffold region can be designed to affect the concentration, location and activity of fluids, factors, molecules or other biologically active agents received from, or delivered to, the extracellular fluids, especially synovial fluid.
- the device provides means to regenerate a first specific form of tissue.
- a tissue specific second scaffold region may be attached to the first region for controlled migration of osteoblasts and/or bone precursor cells.
- an embodiment of the device is a biphasic device, wherein the device consists of two main parts, the cartilage region, and the subchondral bone region, which are joined at an interface surface. Additionally, an embodiment provides a means for deep bone mechanical stimulus by conduction of mechanical and/or fluid forces originating in, or being applied to the cartilage specific scaffold region. These stimuli will be conducted through the subchondral bone region into the adjacent uninvolved subchondral bone.
- the cartilage region can be joined or bound to the subchondral bone region of the device by a number of processes, including but not limited to, heat fusion, heat welding, adhesives, glues or solvent welding.
- the resulting union between the two architectural regions is preferably very strong and can withstand any handling required to package the device as well as any forces delivered to it as a result of the implantation technique without permanently distorting the device's internal architecture of void spaces.
- the interface surface between the two regions may be a permanent or temporary barrier to the passage of cells, fluids, or biological components (e.g. growth factors, proteins, cells signals, etc.) so long as it does not interfere with the transmission of mechanical stimuli resulting from compression of the first region.
- biological components e.g. growth factors, proteins, cells signals, etc.
- the ingrowth or formation of tissue would be specific to the device region, that is, cartilage tissue would grow into the cartilage region of the device, and bone tissue would grow into the bone region of the device based upon the cells within the immediately adjacent tissues, as well as mechanical and chemical signals provided by the individual layers of the device.
- each of the cartilage regions and bone regions may provide for a physical structure that is appropriate to the type of tissue for which it is providing a substrate.
- the bone region will provide a stable substratum for attachment of bone or bone forming cells, while the cartilage region will provide a malleable elastic substratum capable of allowing the surrounding uninvolved tissue to mediate, or affect, the compression and motion of the scaffold adjacent to the host tissue.
- additives capable of enhancing the growth of the target tissue are contemplated within the current invention.
- Additives in the bone region can include ceramics, glass, glass-ceramics, bioactive glasses, as well as biologically active agents.
- Additives in the cartilage region can include gelatinous materials, as well as biologically active agents.
- the additives may be initially loaded into the cartilage region for interaction internally within the device and/or for external device delivery. Additionally, additives can originate within the synovial fluid and be passively or actively transported into the cartilage region of the device.
- Non-limiting examples of materials and additives useful in construction of the various embodiments of the devices described herein can be found in Table 2.
- each device region may be formed utilizing established techniques widely practiced by those skilled in the art of medical grade polymers. These methods may include injection molding, extrusion and machining, vacuum foaming, precipitation, sintering, spinning hollow filaments, solvent evaporation, soluble particulate leaching or combinations thereof. For some methods, plasticizers may be required to reduce the glass transition temperature to low enough levels so that polymer flow will occur without decomposition.
- additives such as plasticizers or particulates can be added to polymers to make them more or less malleable (malleable materials can be elastic as defined earlier or plastic wherein they do not return to there original shape after deformation) in order to provide the desired mechanical properties for the specific device region they will be located in.
- a normally rigid polymer may incorporate a plasticizer to make it malleable and thus useful in the cartilage region whereas rigid particles could be added to a malleable polymer to provide a stable substratum suitable for use in the bone region.
- the osteochondral repair device will be formed as a plug, typically circular in cross-section, and shaped to fill a void or defect created through the cartilage layer and into the underlying bone. Additionally, it is recognized that the plug may have a tapered form, such that one end of the device is larger than the other.
- a defect suitable for accepting the device can be created in a manner known to those skilled in the art, for example, using the device as described in U.S. Application No. 11/049,410, or alternatively using defect creation techniques known as the OATS procedure.
- alternative shapes other than cylinders, may be utilized, v for example joining or overlapping circular elements together into one larger shape will allow for larger defect areas to be repaired with coring tool devices suitable for smaller defects (e.g., approximating an oval, figure eight or a cloverleaf shape).
- non-circular shapes may be utilized as well, such as by providing plug devices with alternative cross-sections, for example, polygonal shapes may be employed or combined (e.g. rectilinear, triangular, hexagonal, etc.), as the polygons may be joined alongside other devices to form a mosaic covering a larger area than could a single device.
- the implant device is prepared for implantation.
- the implantable device may be directed into the void through arthroscopic means, or alternatively by hand into the exposed bone void.
- the device is loaded into an insertion tool.
- any known insertion tool or mechanism may be employed, it is envisioned that the delivery can be accomplished with an insertion tool including a device-containing barrel with a delivery end, and also a plunger extending into the barrel for ejecting the device out the delivery end, in a manner similar to a wide mouth syringe.
- the insertion tool is then placed adjacent to the opening, or directed into the opening, and the device is then ejected from the delivery tool, into the bone void.
- care is taken, both in the creation of the void, and in the delivery of the device, to avoid damaging the healthy nearby tissue, particularly the cartilage tissue and chondrocytes.
- biodegradable, degradable, bioresorbable, resorbable, bioerodable and erodable may be used interchangeably.
- tissue repair device as described herein may be implanted dry, or hydrated with biologically relevant fluids, for example, saline, blood, bone marrow aspirate or Platelet Rich Plasma (PRP).
- biologically relevant fluids for example, saline, blood, bone marrow aspirate or Platelet Rich Plasma (PRP).
- growth factors, hormones, drugs, cells or other useful biologically active agents can be used to hydrate the device. These materials can provide therapy to the cells migrating into the implant, the surrounding tissue, or the synovial fluid.
- growth factors, hormones, drugs, cells or other useful biologically active agents can be located within the synovial fluid and adsorbed into the implant by passive or active means.
- Table 1 a non-exhaustive list of biologically active agents that may be incorporated into at least a portion or the entirety of the various embodiments contained herein can be found in Table 1.
- the encountered loads due to natural movement and gravity are able to be transmitted or conducted through the soft tissues of the joint, and into the hard bony tissues.
- the load transmission is largely vertical, being in the direction of load application, and creates compression of the soft tissue, however, due to the interconnectivity of the soft tissues, particularly across the transverse layer of the articular cartilage, some portion of the loads are distributed laterally as well, to adjoining soft tissue.
- the device is bioresorbable and also supports the growth of new tissue
- the device can avoid the dimpling failure mode seen in prior art devices, as a portion of the device becomes structurally incompetent, the newly grown and structurally competent tissues can provide the required weight bearing ability as well as the ability to transmit mechanical stimulus.
- One embodiment is intended to address the previously described dimpling failure modes, where, it is believed, a portion of the repaired defect area collapses prior to the growth of structurally competent tissue. It is believed that the collapse manifested as dimpling at the surface of the repair site, is a result of failure in either, or both of, the remaining structures of the implanted device, or in the new tissue ingrowth replacing the device as it degrades.
- This embodiment alleviates this occurrence by providing for a resorbable implant structure that fosters satisfactory and controlled tissue ingrowth, and provides for the last invaded and absorbed portion of the device to be degraded after the tissue growth in the device is able to withstand and transmit the encountered loads, also termed "structurally competent".
- Figures 1-6 depict various gradient formations that may be employed within a cartilage region of a biphasic device, that could allow for competent tissue growth to be achieved as the device is degraded and ultimately absorbed, thereby avoiding a mechanical failure of the device caused by collapse or dimpling of the central portion of the newly established tissue within the cartilage region.
- a device having at least one controlled gradient in the device that is arranged concentrically around a vertical axis and normal to the cartilage surface.
- This circular gradient may provide, for example, for a longer duration of implant structural competence as tissue grows in concentrically (or in the form of accelerated tissue regeneration from the outer zone) and spreads to the inner zone depicted at the center of the device and whereas the zones depicted in the outer portion of the device allows for rapid cell invasion and the inner central zones retard cell invasion, or extracellular matrix deposition, until such a time as the cells in the outer zones have laid down the appropriate extracellular matrix, influenced by the mechanical reaction to loading of the uninvolved adjacent cartilage, in the form of hyaline cartilage. It is important to prevent the occurrence of tissue formation as isolated islands, which are not in contact with the uninvolved normal articular cartilage, as isolated islands will not receive appropriate mechanical stimulus from the surrounding uninvolved tissue.
- the controlled circular gradient in the device of Fig. 1 is termed a "bull's-eye" gradient.
- the "bull's-eye” gradient refers to the way the device appears when viewed from the cross- sectional direction depicted in Fig. 2.
- the bull's-eye gradient consists of a central core region or zone 300, surrounded by one or more annular rings. In this depiction, there are two annular rings, 100 and 200, concentrically arranged about the central core.
- the controlled gradient depicted in Fig. 1 with the cross section as shown in Fig. 2 is uniform throughout the length of the device. It is also contemplated that the gradient could vary along the vertical axis, for example, differing in dimension to provide non-uniform cross-sections throughout the length of the device, as can be seen, for example in Fig. 3 and Fig. 4.
- the gradient has two annular rings 110, and 210, surrounding a core region 310.
- the gradient has two annular rings 120, and 220, surrounding a core region 320. It is recognized that the gradients depicted by the figures may exist within a separate structural element in the form of a cylinder or disk
- Gradients can fall into many different groups including but not limited to concentration, chemical, physical and material.
- the invention can be provided in a great variety of useful shaped devices, as will be discussed later, where the gradients of the invention may be created by varying one or more of a variety of characteristics, including porosity, density, molecular weight, cross-linking, hydrophobicity, hydrophilicity, polarity, drug concentration, drug delivery, material, expansion, swelling, elasticity, hardness, compressibility, crystallinity, cell seeding, etc.
- characteristics including porosity, density, molecular weight, cross-linking, hydrophobicity, hydrophilicity, polarity, drug concentration, drug delivery, material, expansion, swelling, elasticity, hardness, compressibility, crystallinity, cell seeding, etc.
- Controlling the density of specific regions of the device may be useful to provide greater structural resistance to compressive loads.
- a gradient can be constructed where the center of the device has a higher density then the outer edge.
- the density change may be achieved, for example, by varying any of the porosity, pore size or pore number in each region of the device, or by varying the molecular weight of the polymer in various zones.
- the device may provide higher density polymers or less porous scaffolding at the center zone 300, and then further removed from the center to the perimeter on the cross-sectional plain of the device, the material becomes less dense and more porous.
- This embodiment with high porosity at the outer zone 100 allows for the cells to migrate quicker initially at the outer zone100, but retards their ability to reach the central zone 200 and inner zone 300, thus concentrating the cells in the outer zone 100.
- Central zone 200 will have a porosity or density in between that of the interior and exterior of the device. This will also extend the duration of structural competence at the core, as the mechanical strength of the core is elevated due to the increased density, and can thus be tailored to stay above a minimum threshold value (as determined by the expected physical loading in the defect area) for a longer period of time, as the device goes through biological degradation.
- the increased duration of structural competence at the center zone 300 allows more time for tissue to infiltrate, grow, and become structurally competent in the core of the device, prior to the total degradation or structural collapse.
- Those skilled in the art will recognize other types of gradients that can be used to decelerate cellular migration, as will be discussed.
- An embodiment of the device may provide for a gradient by using biologically active agents (e.g., drugs, cells, growth factors, etc), ceramics, glass, metals or polymers, all of which are included in the term "additives" incorporated into the device.
- biologically active agents e.g., drugs, cells, growth factors, etc
- ceramics, glass, metals or polymers all of which are included in the term "additives” incorporated into the device.
- the outer zone 100 of the device may provide an elevated additive concentration, relative to the additive concentration provided at the central zone 300 of the device.
- growth factors or other agents that will enhance cellular chemotaxis and growth, this high
- concentration in the outer zone 100 will help recruit cells to the outer edge of the device faster and can increase tissue regeneration at the exterior of the device, resulting in a shorter time period to reach structural competence as the new tissue continues to grow into the middle zone 200, and then into the core zone 300.
- Controlling the rate of cross-linking of the polymer in specific regions of the device may be useful to provide greater structural resistance to compressive loads.
- a gradient can be constructed where the innermost zone 300 of the device has a higher percentage of cross-linked polymers than the outer zone 100 with middle zone 200 having a percentage of cross-linked polymer somewhere in-between.
- the polymer will be more stable under loads, and less subject to biodegradation and bioresorption, resulting in a longer duration of structural competence in the more extensively cross-linked regions, relative to the lesser cross-linked regions of the device.
- the core zone 300 may be a highly cross-linked polymer, and transition to outer zone 100 that is not cross-linked at all, or features less cross-linking.
- mechanical signal transduction is "critical to differentiation of the newly forming tissue, any device having a cartilage scaffold matrix greater in stiffness than the surrounding host tissue will not be influenced by mechanical signal transduction and will either form calcified tissues or
- the device as described herein is intended to set up the best circumstances to allow for the formation of the correct tissue type.
- Controlling the compositional makeup of specific regions of the device may be useful to provide regions with longer durations of structural competence.
- a gradient can be constructed by controlling the polymer blend ratio in each of the zones to provide varying mechanical strength, or degradation rates.
- the innermost zone of the device may be manufactured with a polymer or a blend of polymers that provides enhanced resistance to . degradation, or increased mechanical strength, when compared to the polymer, or blend of polymers provided in the outer zone of the device.
- the center core of the embodiment will feature an enhanced duration of structural competence relative to the outer zone of the device
- natural polymers such as collagen may be used to create regions with varying durations of structural competence.
- the outer zone 100 of the device can be constructed from soluble collagen that posses no fibers and is gelatinous by nature. This allows for more rapid cellular tissue ingrowth to the outer region of the device as the collagen has a low compressive modulus and/or degrades at a rapid rate allowing the newly recruited cells to be stimulated by the mechanical forces necessary to lay down the appropriate tissue matrix.
- the middle region 200 of the device may be constructed from fibrillar collagen. Being of a higher hierarchical structure the fibrillar collagen provides greater structural integrity and/or greater resistance to degradation.
- the collagen may be fibrous, thereby providing even greater mechanical properties and/or greater resistance to degradation than either of the outer zones.
- a gradient can run through the spectrum of gelatin, soluble collagen, fibrillar collagen, fibrous collagen and collagen in the form of decellularized tissue, with or without its extracellular matrix components, some or all of which can be cross- linked as a tool for further control.
- the gradient could be based on length and/or thickness and/or density of fibrils or fibers.
- a homogenous soluble collagen disk may contain an additive such as collagen fibers with the mass or density of the collagen fibers increasing as one proceeds or travels from outer zone 100 towards inner core 300.
- Collagen gradients, as well as other material gradients may also be the result of differing animal sources (bovine, porcine, equine, etc), or use of genetically engineered collagen, for instance from plant sources.
- Regions with varying durations of structural competence may also be achieved with different types or species of polymers from natural or synthetic sources.
- outer zone 100 can be made from hyaluronic acid, which is very easily degradable, while the middle region 200 can be constructed from natural polymer that is more resistant to degradation such as collagen.
- the inner core 300 may contain an even tougher polymer such as chitosan.
- Non- limiting examples of materials and additives useful in construction of devices described herein can be found in Table 2.
- It is recognized that various embodiments of the device may provide more than one gradient, examples of which are depicted in Figs. 5 and 6. In these multi-gradient
- a pair of gradients are created, a first bull's-eye gradient may extend from its widest dimension at the upper surface, and as one travels down the vertical axis, the bull's-eye of the first gradient is shown to diminish in cross-section, ultimately contracting to a point where the zones merge.
- the second gradient may extend from the lower surface, and diminish in area as one travels up the vertical axis.
- the first gradient has two annular rings 130, and 230, surrounding a core region 330
- the second gradient has two annular rings 140 and 240, surrounding a core region 340.
- the second bull's-eye gradient has its largest dimensional area at the lower surface, and as one travels up the vertical axis, the bull's-eye gradient forms around the cone formed by the first bull's-eye gradient described previously.
- the outer dimension of the second gradient is shown to remain uniform, while the inner zone of the second gradient forms as an annular ring surrounding the cone of the first gradient.
- the second bull's-eye gradient regions merge into a narrow annulus, preferably at or near the upper surface of the device.
- the first gradient has two annular rings 150, and 250, surrounding a core region 350
- the second gradient has two annular rings 160 and 260, surrounding a core region 360.
- the second gradient is created as an inverse to the first gradient, and has its largest dimension at the lower surface, and as one travels up the vertical axis, the bull's-eye of the second gradient is shown to reduce in cross-section, ultimately reducing to a point where the zones merge.
- the first and second gradients are composed of unrelated characteristics or materials, and the presence of one gradient will not necessarily interfere with the presence of the other, thus they can be seen to overlap or extend into each other as depicted in Fig.
- these gradients might exist within a device having the gross shape in the form of a cylinder.
- a plug device having a uniform porosity with one of the gradients being a first biologically active agent, and the other gradient being a second biologically active agent.
- one of the gradients may include a structural gradient (e.g., density, cross-linking, etc.)
- the gradients can be employed to optimize the balance required between promoting rapid cell regeneration and tissue competence, against the required need for adequate mechanical competence of the device as well as regulating the rate of device degradation, which is so important to the success of the device.
- the first gradient could preferably be a density gradient, such as can be created by controlling the porosity, pore size, pore density, or polymer molecular weight
- the second gradient could preferably be an additive gradient (e.g., growth factors, drugs, ceramics, cells, etc.)
- This extra area not pictured can be filled, for example, with highly porous polymers that aren't required to provide any structural competence properties, and whose main objective would be to receive host cells and thus promote more rapid tissue regeneration in the external regions closest to the uninvolved host tissue. That is, for the external regions where little or no structural competence is required to be provided by the device allowing the uninvolved adjacent host tissue to mechanically influence the region, it is preferable to provide a material that maximizes the amount and extent of cellular ingrowth into the exterior of the device, in order to provide a foothold of structurally competent tissue within the device as quickly as possible.
- the gradient be formed by altering some material or property within the device in a manner corresponding to the patterns depicted in the figures. Starting from the innermost zone at the core and transitioning through the intermediate zones out to the outer region, the gradient would provide some characteristic that varies as one moves further out from the center. For the sake of simplicity and ease of visualization, much of the explanation in this application only discusses the example of Fig. 1 , however, it is recognized that the teachings of this application also are applicable to the other examples and figures contained in this application as well.
- the gradient may feature zones delineated by the concentric annular rings that provides a recognizable or detectable border or interface between each of the differing zones presented by Fig. 1.
- a continuous transitional gradient or gradual circular gradient could be provided, where there is a gradual change in the characteristic, from the core region and progressing out to the outside
- a device providing for the various gradient characteristics described herein could be manufactured as an intact device, using carefully controlled lyophilization techniques for creating these gradients.
- a series of components may be manufactured, each varying in a particular characteristic. Subsequently, the components may be shaped to a form, where each component will form one of the zones, and thereafter be assembled into a final device.
- a core piece could be manufactured, and later inserted into annular rings sized concentrically, where each of the assembled components will create the gradient desired in the final device.
- one component may be provided as a scaffold material in the manufacture of the other components, thereby forming a multi-zoned device providing a gradient characteristic.
- An example of this manufacturing method would include the injection molding of a central skeleton followed by the incorporation of other less dense open-celled matrices whose densities progress from the central structure outward towards the perimeter of the finished device.
- gradients could be made or created by compressing a starting porous polymer matrix to collapse or sacrifice pores and thus develop a device having the various zones as previously described.
- these gradients could be developed by starting with granulated material, and then through the use of heat and compression, could yield a finished device containing varying porosities and physical shapes.
- fine granular material having an average diameter less than 50 microns can be placed in the center of a cylindrical mold creating a central core. Around this can be pored a medium granular material having an average diameter in the range of 50-100 microns creation a middle zone. A course granular material having an average diameter exceeding 100 microns in turn will surround this. Compression and heat may then be used to fuse this granular material together to create a bull's-eye gradient device.
- the cartilage region of the current invention could be made to expand after implantation.
- the device would provide intimate contact with the surrounding uninvolved cartilage tissue that has retracted away from the defect hole, as the removal of a circular defect from normal articular cartilage has been observed to result in differential retraction of the edges.
- the edges retract more in the superficial zone as compared to the deeper zones after a circular defect is removed with a punch.
- Normal human cartilage, with an intact superficial zone curls when removed from the underlying bone. The retraction away from the defect site, as well as the curling of the removed cartilage, is the result of the high tension existing within the superficial zone of articular cartilage.
- Applicants have made an additional surprising discovery that in effecting the repair of cartilage defects, prior art synthetic implants and synthetic bi-phasic implant devices failed to recognize the importance of synovial fluid in the maintenance and repair of articular cartilage.
- As an additional consideration in the development of a device for repair of articular cartilage one needs to understand how friction, cyclic motion, electric potential and synovial fluid all work together to maintain the articular cartilage phenotype. Under normal physiological conditions, articular cartilage provides a nearly frictionless surface between moving joint. To help lubricate these joints, the body uses synovial fluid. This fluid component consists primarily of water with dissolved solutes and mobile ions.
- Solute transport in biological tissues is a fundamental process of life, providing nutrients to cells and carrying away waste products.
- solute transport occurs primarily across the articular surface, with synovial fluid mediating exchanges with the synovium lining the joint capsule.
- a primary mechanism of solute transport is through diffusion.
- the mechanism of passive diffusion in healthy cartilage has been shown experimentally to be enhanced by cyclical loading of the cartilage, and by electro-osmotic flow both, of which mechanisms lead to convective flow within the tissue.
- avascular tissue types that respond similarly to articular cartilage include tendon, ligament, meniscus and annulus thus the techniques described herein for use in cartilage repair by manipulating the natural fluid and electric potential in the region may be used on these other tissue types as well. It is also envisioned that these techniques could be beneficial on vascularized tissue that are elastic in nature, including but not limited to blood vessels and skin.
- the synovial fluid acts as a transport medium for substances into and out of the articular cartilage region. This is necessary because the articular cartilage region is a non-vascular tissue. Substances are transported into and out of the articular cartilage region due to repetitive mechanical stimulus followed by a period of rest. During active mechanical stimuli, molecules located within the synovial fluid are actively transported into the articular cartilage layer. This allows the concentration of molecules within the cartilage tissue to exceed that of the synovial fluid. During rest, the concentration will return to equilibrium. In this way, necessary substances located within the synovial fluid are forced into the cartilage tissue, whereupon the cells can absorb them.
- Waste products are excreted by the cells into the interstitial space of the tissue where they build up. During a period of rest, the system moves towards equilibrium and thus the waste products move out of the cartilage tissue and into the synovial fluid wherein they are ultimately transported into the vasculature and away from the knee.
- a preferred form of the current invention allows for uniform incorporation of necessary target molecules by providing a biodegradable, insoluble malleable elastic gel or hydrogel like substratum containing a sufficient concentration of fibers so that they form a penetrating interconnected phase.
- the gel or hydrogel can also present an interconnecting porosity.
- the fibers, making up a second phase can be entangled, entwined, interwoven, knitted or in some other fashion connected in a three-dimensional web or matrix so that stresses in the form of a push or pull are telegraphed throughout the entire device. In this way the current invention is capable of receiving joint fluid therapy throughout its entire volume.
- Figure 7 represents prior art biphasic device 700 having a cartilage region of simple pores, or in the form of a gel.
- pressure waves 730 remain focused just below original force 710.
- FIG 8 which depicts a cross-section of biphasic device 800 wherein connected fibers 810 are located within layer 820.
- force 830 is applied to the surface of layer 820, downward pressure force 830 causes connected fibers 810 to pull on each other, telegraphing pressure force 830 throughout the entire volume of layer 820, creating a circular force, vortex, vortex ring, toroid, or gyre, as represented by arrows 840.
- the described circular force occurs three-dimensionally establishing a vortex ring, that is, multiple vortexes or gyres within the device.
- the potential vorticity of fluid within the device is directly related to the volume of displacement within the device matrix from the downward pressure force. In the simplest sense, vorticity is the tendency for elements of the fluid to "spin.” and can be related to the amount of "circulation” or “rotation” in the fluid contained in the matrix caused by the gyres.
- forces applied to cartilage tissue distant from the device will be transmitted through the host tissue and into the device.
- the cartilage layer of an embodiment of the device will be composed of at least two phases.
- This first phase is an insoluble gel or hydrogel capable of adsorbing and concentrating target molecules from the synovial fluid when placed under repetitive compressive forces.
- the second phase will be a fibrous component associated with or contained within the gel phase having sufficient connectivity so that a compressive force applied to one location of the cartilage layer is transmitted throughout substantially the entire volume of the cartilage layer.
- the minimum average fiber length for fibers randomly located within the gel should be approximately equal to the thickness of articular cartilage, which is from 2 - 3 millimeters in length.
- the maximum average fiber length should not exceed 1.5 times the diameter of the devices so as to prevent curling or coiling of the fibers preventing them from being taut within the matrix and thus dampening the transmission of mechanical stimulus.
- These same length restrictions apply to interwoven or knitted type devices in as much as connecting nodes or knots holding the structure together should be no closer than 2 - 3 millimeters apart and no farther apart than 1.5 times the diameter of the devices.
- the average length of the fibers would be in the range of 2 - 15 mm, and the average distance between connecting nodes or knots would be in the range of 2 - 15 mm.
- the material phases can be fabricated from natural and/or synthetic polymers including but not limited to collagen, elastin, keratin, chitosan, hyaluronic acid, silk, alginate, polyethylene glycol (PEG) and combinations thereof. (Non-limiting examples of materials and additives useful in construction of devices described herein can be found in Table 2.)
- One or more of the phases can also contain biologically active agents such as those listed in Table 1.
- the biologic activities of the chondrocyte population are regulated by genetic, and other biologic and biochemical factors, as well as environmental factors. It has often been noted that physical environmental factors, such as stress, fluid flow, electric fields, etc. are as strong as biologic factors in regulating cellular activities.
- the electromechanical signals that chondrocytes perceive in situ are the result of stresses, strains, pressures and the electric fields generated inside the extracellular matrix when the tissue is deformed.
- the potential induced by convection in the presence of a pressure gradient in deformed tissue is the "streaming potential”.
- the potential induced by diffusion in the presence of a concentration gradient in static tissue is the "diffusion potential”.
- Avascular tissues such as cartilage are composed of water, collagen enmeshed in a proteoglycan gel, and various matrix proteins.
- the osmotic pressure of these tissues is mainly due to the high density of charged carboxyl and sulfate groups on the glycosaminoglycans of the proteoglycans within the tissues.
- interstitial fluid flow occurs, even though the hydraulic permeability of the tissues is very low.
- the electrical response of the tissues also changes when it is compressed due to the effects of diffusion potential and streaming potential.
- the diffusion potential is the electric potential caused by the separation between the bulk positive and bulk negative charges caused by the gradients of mobile ions within the different fluid regions of the tissue or between the tissue fluid and the synovial fluid.
- Streaming potential is defined as the difference in electric potential between a diaphragm, capillary, or porous solid and a liquid that is forced to flow through it.
- the definition of streaming potential can also include the difference in electric potential caused by the oscillation, separation or flow of a gel in relationship to a diaphragm, capillary or porous solid. Specifically, it is the potential that is produced when a liquid or gel is forced to flow through a capillary or a porous solid.
- the streaming potential is one of four related electrokinetic phenomena that depend upon the presence of an electrical double layer at a solid-liquid/gel interface.
- This electrical double layer is made up of ions of one charge type that are fixed to the surface of the solid and an equal number of mobile ions of the opposite charge which are distributed through the neighboring region of the liquid/gel phase.
- the applied potential necessary to reduce the net flow of electricity to zero is the streaming potential.
- Streaming potential is related to zeta potential by factors that include the electrical conductivity and fluid/gel viscosity. The value of streaming potential under given conditions of conductivity and pressure can be used to judge how strongly the tissue will interact with anionic or cationic molecules.
- the zeta potential is a good predictor of the magnitude of electrical repulsive force.
- a resulting voltage is measured between electrode probes on either side of a boundary. This voltage is then compared with the voltage at zero applied pressure.
- the source of electrical events derives from the fixed, immobilized or trapped negative charges ⁇ SO3 and COO2, distributed along the chondroitin, keratin sulfates and hyaluronan molecules making up the aggrecan inside the extracellular matrix of the tissue.
- These proteoglycans may be assumed to be "immobilized and trapped” inside the extracellular matrix, and therefore considered to be fixed to the extracellular matrix. Together with the surrounding collagen network, these proteoglycan macromolecules form the cohesive, strong, porous-permeable, charged, collagen/proteoglycan solid matrix.
- both streaming potential and diffusion potential must always exist inside the tissue and in fact they always compete against each other.
- the streaming potential arises from the slight separation of the bulk of the positive charges from that of the negative charges due to the flow convection effects caused by a pressure gradient from deformation of the tissue.
- the diffusion potential arises from the slight separation of the bulk of positive charges from that of the negative charges due to diffusion caused by the gradients of mobile ions. It is believed that electrical events inside the tissue are important in stimulating chondrocyte biosyntheses.
- the cartilage layer of this preferred device will be composed of at least two phases.
- This first phase is an insoluble gel or hydrogel capable of adsorbing and concentrating target charged molecules from the synovial fluid when placed under repetitive compressive forces.
- the second phase will be a fibrous component contained within the gel phase having sufficient connectivity so that a compressive force applied to one location of the cartilage layer is transmitted throughout the entire volume of the cartilage layer. This allows creation of a disparity between the overall charges of the synovial fluid from that of the cartilage layer establishing the diffusion potential.
- the first phase In addition to this it is desirable for the first phase to predominantly contain either positive or negative charges while the second phase will predominantly contain charges opposite that of the first phase. In this way a pressure gradient from deformation of the cartilage layer of the preferred embodiment creates a slight separation between the charges of the first phase from that of the second phase, as the gel and fibers flex, thus establishing the streaming potential. If desirable, one or both phases can be cross-linked. Thus the electric potentials created by such an embodiment simulate that which occurs in normal articular cartilage, thus improving and/or stimulating chondrocyte biosyntheses and thus articular cartilage tissue formation.
- insoluble collagen fibers are exposed to a more basic chemical environment (above the pH of the collagen's isoelectric point) in order to bring the surface of the collagen above its isoelectric point and thus providing a predominantly negative charge to the surface of the fibers composing the second phase of the devices.
- These negatively charged fibers are embedded within a collagen gel or hydrogel that was exposed to a more acidic chemical environment (below the pH of the collagen's isoelectric point) so as to drive this collagen below its isoelectric point to provide a
- biodegradable polyester fibers ie -PLA, PGA, PCL, etc
- surface modifications such as exposure to acids, bases, or plasma gas processes
- hyaluronic acid gel or hydrogel having a predominantly negative charge is used as the first phase that encapsulates and surrounds a second phase of chitosan fibers having an overall positive charge.
- PEC polyelectrolytic complex
- an electrically neutral hydrogel first phase envelops a charged fibrous second phase, wherein the gel allows mobile ions to penetrate and take up residence within the gel thus balancing out the charge of the fibrous second phase.
- an electrically neutral hydrogel would be a PEC.
- PEC Such a PEC could be manufactured by various techniques known in the art, incorporating known
- the neutral hydrogel PEC could be created by the combination of charged components, such as hyaluronic acid - chitosan, collagen - chitosan, and hyaluronic acid - collagen.
- the second phase material can be composed of particulate materials that are not fibrous or polymeric in nature so long as they provide the necessary charged surface.
- a non-limiting list of materials suitable for this use can be found in table 2.
- part of the function of the device is to transfer forces or loads, experienced by the cartilage layer, through the devices and into the subchondral bone. This deep bone mechanical stimulus is necessary to prevent stress shielding that currently results in bone voids below the device.
- Figure 9 shows 12-month histology from a prior art device that provided stress shielding to the underlying bone. Box 910 shows the approximate location of the implant that has completely resorbed. Soft tissue void 920 within the bone is the result of this stress shielding.
- both cartilage and bone are living tissues that respond and adapt to the loads they experience. If a joint surface remains unloaded for appreciable periods of time the cartilage tends to soften and weaken. Further, as with most materials that experience structural loads, particularly cyclic structural loads, both bone and cartilage begin to show signs of failure at loads that are below their ultimate strength. Research into bone healing has shown that some mechanical stimulation can enhance the healing response and it is likely that the optimum regime for a cartilage/bone graft or construct will involve different levels of loading over time in order to properly repair a damaged region. This same observation was concluded by Surgeon Julius Wolff back in the 19 th century and is still known today as Wolff's law.
- the cored hole will exhibit a very uniform cylindrical shape, however, the bottom surface may be inconsistent and have a rather jagged and irregular surface. This can create gaps or void pockets under the implant or create a void between the top of the implant and the mating rotating bone and prevent any transfer of forces or pressure during the healing process.
- the surgeon is concerned about protrusion of the harvested plug creating too much pressure on the transplanted hyaline cartilage thereby damaging this tissue as the joint moves.
- the surgeon often creates a deeper recipient site defect then the length of the harvested plug. This allows the surgeon to control the final position or height of the implanted device; however, this is assuming that the frictional forces alone will provide enough stability for the plug to stay in position. This also creates a void space under the implant, which prevents contact from occurring with the subchondral bone.
- a device could be designed so that a portion of it has the ability to expand and contract like an extension spring. Once the device is implanted into a cored hole, the expansion and contraction of the implant would provide the proper functionality. In addition, it is desirable to also create sufficient contact with the walls of the cored hole.
- a cartilage/bone repair device is envisioned which takes into consideration the transfer of structural loads or pressures that may be seen by the implant once it is installed into a cored- out hole in the recipient's bone.
- the implant may be made of different materials or different forms of the same material.
- a rigid support skeleton can be injection molded from a PLA polymer and this same polymer can be chemically processed to create an open- celled foam structure. Both of these materials would act in completely different ways in regards to their absorption characteristics, their load transfer characteristics, and their biological cell attraction characteristics.
- the implant may include various means of securing itself within the area of bone repair.
- These securing means can include mechanical methods such as teeth or ridges that are incorporated around the outside surfaces of the device. These teeth or ridges can also assist with the transfer of forces through the device and into the surrounding bone.
- the device could utilize different characteristics formulated into the structural make up of the device in order to promote the take up of fluid thereby causing a hydraulic effect in a portion of the device, which would create a means of expansion and thereby allow for pressure to be transferred through the device.
- the device contains fluid swellable expansion zones that provide for a tight fit within the void and allow for micro-motion while other porous stable zones allow for cell attachment and tissue growth.
- device 1000 has center column 1010 positioned under cartilage layer 1020 that transcends down the center and then transitions to a larger diameter at the bottom to allow the transfer of force or pressure between the upper surface of the implant and the implant/bone interface layer at the bottom of the device.
- Porous matrix 1030 surrounds center column 1010 and makes contact with the host tissue.
- Center column 1010 can be porous, but is rigid and thus conductive of mechanical stimulus that would be dampened by porous matrix 1030. It is preferable that porous matrix 1030 swells shortly after placement into the tissue void so direct contact is made with the tissue void walls.
- center column 1010 can also transition to a larger diameter at the top (not shown), presenting an hourglass type of shape. Additionally, center column 1010 can be formed from a small diameter cylinder with a thin flat plate on the bottom and optionally the top (not shown). The porosity, if present, in center column 1010 can be random, or in the form of elongated channels capable of conducting hydraulic forces.
- Figure 11a shows device 1100 having multi-facetted web structure 1110 that is oriented perpendicular to the top and bottom surfaces of device 1100.
- the web acts as a stiffener to transfer the load originating in cartilage layer 1120 through the implant.
- Secondary material 1130 is a less dense, more porous structure formed in between the spokes of web structure 1110.
- Figure 11b shows a top down view with the cartilage layer removed so that the relationship of the spokes of web structure 1110 and secondary material 1130 can easily be visualized.
- the web would continue to transfer the forces into the subchondral bone region while bone growth was occurring within the porous structure of secondary material 1110 found in between the webs or spokes of web structure 1 110. As bone growth completed the encroachment of this area, it would assist with the load or pressure transfer while the materials of web structure 1 1 10 started its degradation and eventual removal.
- Web structure 11 10 can have holes or slots within its structure to allow intercommunication of the secondary material 1130.
- device 1200 has conically shaped center post 1210 sitting below cartilage layer 1220.
- Center post 1210 wedges into outer cylinder layer 1230 possessing a shaped inner cavity designed to receive center post 1210.
- Center post 1210 may extend completely through outer layer cylinder layer 1230 as pictured or may instead just come flush to the base of device 1200.
- the tapered shape of center post 1210 provides for a means of seating the implant while also providing a method for transferring mechanical stimulus to all sections of the subchondral bone region.
- outer cylinder layer 1230 is experiences outward force 1240 thus providing improved seating of device 1200 into a , cored bone void.
- forces applied to cartilage layer 1220 pass into center post 1210 and are transferred to the tissue void.
- Figure 13 is composed of a multi-layered cylinder containing various material thicknesses and densities.
- the layers can be constructed to act to transfer the pressure between the top surface of the device and the bottom surface.
- the composition of these various layers can also be utilized to create hydraulic swelling to thereby create the spring-like effect previously described.
- Figure 14a shows a simplified example of a bone region multi-layered cylinder 1400. To simplify understanding, the cartilage layer is not pictured. Swellable layers 1420 separate rigid porous layers 1410. More or less layers are also contemplated. Upon implantation or exposure to liquid, swellable layers 1420 imbibe fluid and become an uncompressible, flexible hydrogel as depicted in figure 14b where rigid porous layers 1410 are now separated by swollen layers 1430.
- a force applied to the cartilage layer is transferred as a pressure wave through the device so long as rigid porous layers 1410 do not exceed 4mm in thickness and have an average porosity greater than 50 microns and are rigid enough to avoid collapse of their porosity thus not dissipating the pressure wave prior to it reaching the bottom layer and finally being conducted into the underlying bone.
- one or more holes 2 millimeters in diameter or greater can exist in layers 1410 allowing pillars of hydrogel to connect swollen layers1430. It may be I that newly forming bone needs a stable substratum to attach to so that bone forming cells can lay down extracellular matrix.
- Bone forming cells known as osteoblasts are approximately 50 microns in diameter and should establish themselves in newly forming islands of bone approximately 1 mm in diameter, thus the minimum thickness of porous layer 1410 is 1 millimeter.
- the thickness of swollen layer 1430 has no maximum, but should be at a minimum of 5 microns with a preferred thickness of 50 microns to trap a sufficient amount of fluid and thus function as an incompressible hydrogel capable of transferring pressure waves.
- porous particles having a minimum approximate diameter of 1 millimeter can be surrounded by a swellable material wherein the swellable material maintains connectivity throughout the entire device.
- pressure waves and micro motion necessary for establishing bone external to the device, can be conducted through the swellable material matrix while the porous particles provide a stable platform for attachment and proliferation of osteoblasts.
- porous particles composed of ceramic, polymer or composites of the two can be suspended within a hydrogel forming material such as collagen, hyaluronic acid, chitosan, alginate, keratin, or PEG.
- the hydrogel can be formed into a porous network presenting fluid swollen struts or partitions defining fluid containing pores.
- the bone region of all the above devices can be designed so that they provide the required expansion and transfer of force as the materials degrade. This transfer of force can occur through the use of rigid polymeric or ceramic elements, incompressible hydrogels or combinations thereof. As more cells are stimulated to grow into the implanted matrix, newly formed tissue will help to continue the transfer of the mechanical stimulation.
- Angiotensin Converting Enzyme Inhibitors ACE inhibitors
- aFGF acidic fibroblast growth factor
- bFGF basic fibroblast growth factor
- BMP Bone morphogenic proteins
- EGF epidermal growth factor
- GM-CSF granulocyte-macrophage colony stimulating factor
- HGF hepatocyte growth factor
- IGF-I insulin growth factor- 1
- PD-ECGF platelet-derived endothelial cell growth factor
- PDGF platelet-derived growth factor
- TGF-. alpha. transforming growth factors alpha & beta
- TGF-beta. tumor necrosis factor alpha
- VEGF vascular endothelial growth factor
- VPF vascular permeability factor
- BMP Bone morphogenic proteins
- Chemotherapeutic agents e.g. Ceramide, Taxol, Cisplatin
- Cholesterol reducers e.g. Ceramide, Taxol, Cisplatin
- G-CSF Granulocyte-macrophage colony stimulating factor
- Acidic fibroblast growth factor (aFGF)
- bFGF Basic fibroblast growth factor
- BMPs Bone morphogenic proteins
- CDF Cartilage Derived Growth Factors
- EGF Endothelial Cell Growth Factor
- EGF Epidermal growth factor
- FGF Fibroblast Growth Factors
- HGF Hepatocyte growth factor
- Insulin-like Growth Factors e.g. IGF-I
- Nerve growth factor (NGF)
- PD-ECGF Platelet Derived endothelial cell growth factor
- PDGF Platelet Derived Growth Factor
- TNF Tissue necrosis factor
- TGF-alpha Transforming growth factors alpha
- TGF-beta Tumor necrosis factor alpha (TNF-. alpha.)
- VEGF Vascular Endothelial Growth Factor
- vascular permeability factor UPF
- HMC-CoA reductase inhibitors (statins)
- Glycolide/trimethylene carbonate copolymers (PGA/TMC)
- PLA-polyethylene oxide (PELA) PLA-polyethylene oxide
- PCL Poly- ⁇ -caprolactone
- TMC Trimethylene carbonate
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP10732762A EP2448523A1 (en) | 2009-06-30 | 2010-06-30 | Multi-phasic implant device for the repair or replacement of cartilage tissue |
CA2766913A CA2766913A1 (en) | 2009-06-30 | 2010-06-30 | Multi-phasic implant device for the repair or replacement of cartilage tissue |
AU2010266713A AU2010266713A1 (en) | 2009-06-30 | 2010-06-30 | Multi-phasic implant device for the repair or replacement of cartilage tissue |
AU2016201883A AU2016201883B2 (en) | 2009-06-30 | 2016-03-24 | Multi-phasic implant device for the repair or replacement of cartilage tissue |
Applications Claiming Priority (8)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US12/495,611 US10016278B2 (en) | 2009-06-30 | 2009-06-30 | Biphasic implant device providing joint fluid therapy |
US12/495,611 | 2009-06-30 | ||
US12/495,534 US20100331998A1 (en) | 2009-06-30 | 2009-06-30 | Electrokinetic device for tissue repair |
US12/495,688 US20100331979A1 (en) | 2009-06-30 | 2009-06-30 | Biphasic implant device transmitting mechanical stimulus |
US12/495,657 | 2009-06-30 | ||
US12/495,657 US9744123B2 (en) | 2009-06-30 | 2009-06-30 | Biphasic implant device providing gradient |
US12/495,534 | 2009-06-30 | ||
US12/495,688 | 2009-06-30 |
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WO2011002511A1 true WO2011002511A1 (en) | 2011-01-06 |
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PCT/US2010/001878 WO2011002511A1 (en) | 2009-06-30 | 2010-06-30 | Multi-phasic implant device for the repair or replacement of cartilage tissue |
Country Status (4)
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EP (1) | EP2448523A1 (en) |
AU (2) | AU2010266713A1 (en) |
CA (1) | CA2766913A1 (en) |
WO (1) | WO2011002511A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8685106B2 (en) | 2011-11-15 | 2014-04-01 | Abraham Lin | Method of a pharmaceutical delivery system for use within a joint replacement |
WO2015042354A1 (en) * | 2013-09-20 | 2015-03-26 | Indianna University Research And Technology Corporation | Mechanical bone loading to reduce arthritic pain |
CN111840663A (en) * | 2019-04-08 | 2020-10-30 | 上海微创医疗器械(集团)有限公司 | Medicine-carrying implantation medical apparatus and preparation method thereof |
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- 2010-06-30 CA CA2766913A patent/CA2766913A1/en not_active Abandoned
- 2010-06-30 EP EP10732762A patent/EP2448523A1/en not_active Withdrawn
- 2010-06-30 AU AU2010266713A patent/AU2010266713A1/en not_active Abandoned
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WO2000009179A2 (en) * | 1998-08-14 | 2000-02-24 | Verigen Transplantation Service International (Vtsi) Ag | Methods, instruments and materials for chondrocyte cell transplantation |
US20030114936A1 (en) * | 1998-10-12 | 2003-06-19 | Therics, Inc. | Complex three-dimensional composite scaffold resistant to delimination |
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Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8685106B2 (en) | 2011-11-15 | 2014-04-01 | Abraham Lin | Method of a pharmaceutical delivery system for use within a joint replacement |
WO2015042354A1 (en) * | 2013-09-20 | 2015-03-26 | Indianna University Research And Technology Corporation | Mechanical bone loading to reduce arthritic pain |
CN111840663A (en) * | 2019-04-08 | 2020-10-30 | 上海微创医疗器械(集团)有限公司 | Medicine-carrying implantation medical apparatus and preparation method thereof |
Also Published As
Publication number | Publication date |
---|---|
CA2766913A1 (en) | 2011-01-06 |
AU2010266713A1 (en) | 2012-01-19 |
AU2016201883A1 (en) | 2016-04-21 |
EP2448523A1 (en) | 2012-05-09 |
AU2016201883B2 (en) | 2017-11-02 |
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